Last year Matt Meeks bought a new 50 hp blower and variable-frequency drive for the City of Maize (Kan.) Wastewater Treatment Plant. No city official questioned the purchase — because, after all, Meeks had raised the money.
For nearly two years, the Maize plant has accepted partially treated process water from a nearby ethanol plant at a price of five cents per gallon. With potential to receive as much as 2 million gallons of the water per year, the plant could see $100,000 in annual revenue beyond everyday fees from connected customers.
The plant has ample capacity to take the water, and so far it has had no adverse effects on the process.
Outsourcing treatment
The Maize plant, serving a community of about 3,000 residents, is a 0.5 mgd (design) extended aeration activated sludge facility. Average flow is about 0.25 mgd. “It’s a very stable plant,” says Meeks, senior water/wastewater controller for the city. “Our worst headaches are from storm surges: We don’t have an equalization basin.”
In early 2009, the manager of the ethanol plant, half a dozen miles away, approached Meeks to discuss treating the process water. The water contains on average 30 mg/l BOD and 126 mg/l TSS and has a pH of 9 and 8.0 ppm dissolved oxygen.
Meeks says one issue the ethanol plant has is that under state regulations, any rainwater that collects on the plant grounds is classified as process water and goes to the treatment ponds. Rather than refine its own treatment process and discharge the water under its own permit, the facility prefers to outsource treatment and focus on optimizing ethanol production, Meeks says.
Meeks restricts daily deliveries to 50,000 to 60,000 gallons. Deliveries are sporadic and are tied to rain events. The water is delivered in tank trucks. The Maize plant accepted 1 million gallons in 2009 and by the end of June had taken 880,000 gallons in 2010. Trucks empty into the first manhole upstream of the treatment plant’s main lift station pumps.
No upsets
“It seems to work just fine,” Meeks says. “We have the excess capacity, and we have such a long detention time that the plant just seems to assimilate it. The main effect we get is a little green color, which I think is from algae cells lysing.
“We just keep an eye on everything to make sure we’re not heading toward an upset. We watch the effluent ammonias and pH and the plant DOs. Every now and then we sample what’s coming in to make sure it hasn’t changed in some fashion. We use a little more energy to treat the water, and maybe we spend a little more money handling the additional digested solids going out.”
Maize uses Agra Enterprises, a part-time hauling business owned by area farmer Keenan Kelley, to haul its biosolids to land application sites. The same company hauls the process water from the ethanol plant to Maize.
Revenue from treating the ethanol plant’s water is helping Meeks keep plant equipment up to date. Besides the blower and VFD, he has purchased a 3 hp submersible in-plant process pump and rebuilt another.
Looking ahead
At present, the ethanol plant is building a sewer line to deliver the water to the treatment plant. City officials, recognizing the potential value of that line, negotiated with the ethanol company to upsize it to create capacity for expansion. Meeks observes that Maize has grown rapidly since the city installed a drinking water system in 2003.
“I told the city council that what we have here is a prime example of how a well-maintained, well-operated plant is an asset to the community that owns it, to the communities around it, and to the environment,” says Meeks. “The water we discharge is cleaner than what’s in the creek.”
